Less than two weeks ago, the French nuclear regulator, ASN, published a press release on the English part of its web site entitled “The situation regarding nuclear safety and radiation protection is worrying ASN remains vigilant“, 30/01/2017 5:36 pm. In it they quote the ASN Chair, Pierre-Franck Chevet, as having told the press on January 18th that “a year ago, the situation with regard to nuclear installations was worrying in the medium term. If I had to summarize my thoughts today, I would say that the situation is worrying. I omit “in the medium term“. [1]

Unlike the US NRC, the French ASN appears to want to do its job, but is short-staffed, as well as in the difficult situation of being a government department trying to hold majority government-owned (EDF-Areva) companies accountable. This includes the need to watch-dog both old reactors and possible manufacturing defects (both new and old) at Areva Le Creusot. In short, they are in over their heads, but at least they seem aware of this fact and are worried. Up until now, the US NRC appears to lack any such excuses, and shows little concern, though the new US administration may well shut the US NRC down.

Any equipment failure in nuclear power stations cannot be taken lightly. The frightening speed at which equipment failures in a nuclear power station can spiral out of control is illustrated by the Three Mile Island Nuclear Disaster, which was well underway within 2 hours (6 am) of the reactor trip and SCRAM (4 am).[2,4] A nuclear reactor can began to meltdown after only a few hours of loss of cooling.[3]

And, of course, the movie "The China Syndrome" provides a reminder: http://youtu.be/UFMsnicAtiY (trailer) Instead of burning a hole through to China, like the name “The China Syndrome” implies, might an accident at Flamanville, along the English Channel, be called a “Chunnel Syndrome”?

David Lochbaum of the Union for Concerned Scientists explains that "Fire is a major hazard at nuclear power plants because it can, as it did at Browns Ferry, disable primary safety systems and their backups." [5] The Spokesperson for Wise Paris adds that there is a risk that a large enough explosion or uncontrolled fire could impact the nuclear reactor itself. [6]

The French nuclear safety authority, ASN, news release, itself, speaks of a detonation, rather than an explosion. Both words occur in French and English. https://en.wikipedia.org/wiki/Detonation
[Update: Based on the older French nuclear safety authority, ISRN, it was apparently a hydrogen detonation initiated by a fire – see further below. Update 2: The turbine-generator (steam generator) is by ALSTOM and appears to be hydrogen cooled (insanely enough). This seems to be the source of the detonation, based on our understanding of the ISRN and ASN press releases.]

Translation based on Sortir du nucléaire press release, February 9. 2017:
Explosion at the Flamanville Nuclear Power Station: an "incident" which is symptomatic of very degraded safety.

This Thursday, February 9, at around 10 am, an explosion took place in the machine room of the Flamanville reactor no. 1, followed by a large discharge of smoke. Five people suffered from smoke intoxication.

A defective fan was responsible. Given the current state of the information which EDF filters out, it is difficult to evaluate the seriousness of this "incident". However, this problem should not be minimized under the pretext that it took place "in the non-nuclear part of the facility".

Indeed, the simple fact that such an explosion could occur in the machine room indicates an insufficient maintenance or degraded condition of the fan in question. This event is to be put in perspective with the multiplication of fires initiated in electrical equipment in French power plants in recent years, due in particular to the aging of electrical equipment.

Moreover, the consequences of this event are not limited to where the fire started. The reactor n ° 1 had to undergo an emergency shut-down [SCRAM] at 9h47. Not only did residual heat still needed to be evacuated, but a sharp decline in output is never good for nuclear equipment, especially if, for one reason or another, it is already in a fragile state. [1]

Additionally, shouldn't one fear that this explosion could have damaged other equipment, and in any case it would have caused disruption of the power station's activity?

… "Sortir du nucléaire" network again calls for abandoning the construction of the new Flamanville EPR [European Pressurized Reactor] , along with old reactors.
Note [1] One can also wonder about the consequences that such an emergency outage could have if it were to occur at one of the reactors equipped with defective steam generators which were recently authorized to restart. In effect, a sudden temperature change would be contrary to the recommendations of the Nuclear Safety Authority. See original news release in French "Explosion à la centrale nucléaire de Flamanville : un "incident" symptômatique d’une sûreté très dégradée Communiqué du 9 février 2017" here: http://www.sortirdunucleaire.org/Explosion-a-la-centrale-nucleaire-de-Flamanville [In the French original they seem to be calling for shutdown at the end of the originally planned service life. Is this all nuclear reactors in France? If not, any delays could be too late. Europe is still contaminated from Chernobyl and weapons testing. It cannot afford another nuclear accident! Their comment note 1 should not be confused with our reference note 1, found further below.]

In a news release, the ASN explains that EDF (the operator) had to shutdown reactor No. 1 and stated that they will ask EDF to furnish it with a complete analysis of the causes and consequences of the event, somewhat contradicting an earlier sentence stating that the explosion-fire did not affect nuclear safety or the environment.

Translation based on the French nuclear regulator ASN news release of the nuclear "Event" in the machine room at the Flamanville nuclear power plant 1
09/02/2017 17:21 Central European Time news release:
The Nuclear Safety Authority (ASN) was informed this morning that an event occurred at the Flamanville nuclear power plant.

A detonation and the initiation of a fire in a fan located under the steam generator took place on February 9, 2017 at around 9.45 am [CET] in the non-nuclear zone (machine room) of reactor No. 1.

The fire was quickly put under control by the EDF teams.

This event did not cause serious injuries and did not affect nuclear safety or the environment.

The operator initiated the shutdown of reactor No. 1.

The ASN will ask EDF to furnish it with a complete analysis of the causes and consequences of the event. Date of last update was 09/02/2017. [7]
Translation note – The original actually uses the word “detonation”. The word “explosion” also exists in French. Thus, this choice of words may matter. Original ASN phrase: “Une détonation et un départ de feu au niveau d’un ventilateur situé sous l’alternateur“[7]. The alternator is apparently the steam generator (turbine generator), based on the description given. See more below in our endnote [7].

Update – The older regulator, ISRN, has given additional details in a news release. They stated that a beginning (initiation) of a fire causing a detonation (apparently quoting EDF, as the French is in quotes) took place around 10 am, Thursday 9 February,… According to information gathered by the IRSN from EDF, a detonation was heard in the machine room of Flamanville no. 1, which was operating. The detonation was followed by a release of smoke which activated a fire alarm in the control room. All these elements led to the tripping of the turbine, without the automatic shut-down of the reactor. The operators then shutdown the reactor in conformance with procedures, without particular difficulty. Simulataneously, the EDF’s intervention teams were able to quickly control the fire near the alternator [turbine generator/steam generator], subsequently supported SDIS de la Manche (Departmental Service of Fire and Rescue). By noon, the situation was completely under control and the reactor was in the normal shutdown phase. As a preventative measure, the operator proceeded to empty all the hydrogen present in the alternator [turbine generator/steam generator] in order to avoid a new explosion, the hydrogen serving as coolant during operation.

The initial investigations carried out by EDF do not yet explain the origin of the detonation. Several lines of inquiry are currently being explored by the operator (failure of a fan close to the alternator [turbine generator/steam generator] with collateral effects, failure of an alternator [generator] phase, etc.) [8] Note that the original uses alternator, but the translation for turbo-alternateur is turbo-generator. While turbo-generator is used, it is technically inaccurate. It is supposed to be turbine generator. It is apparently the steam generator. For details on the definition of alternator given by the ASN see notes below. Also, notice that the local fire department had to help them, meaning that they would be unavailable to help the community.

Greenpeace France twitter has a tweet showing white smoke discharging from the power station, which actually looks like steam: https://twitter.com/greenpeacefrCould it have been a steam and/or hydrogen detonation-explosion? The better pictures showing the discharge, which looks like white steam, appear to be from AFP. They can be seen doing a search.